1. Field of the Invention
The present invention relates to a thin film magnetic write head and more particularly to a thin film magnetic write head which has a submicron trackwidth.
2. Description of the Related Art
In a magnetic disk drive, data is written and read by magnetic transducers called "heads" which are positioned over a disk while it is rotated at a high speed. Magnetic heads are mounted on sliders that are supported over a surface of the disk by a thin cushion of air (an "air bearing") produced by the disk's high rotational speed. In order to increase the amount of data stored per unit of disk surface area ("areal density"), more data must be written in narrower tracks on the disk surface.
One principal means of improving areal density of magnetic recording is to improve the number of data tracks which a write head can record on a disk; the related parametric expression is "tracks per inch" or "TPI". The TPI capability of a write head is increased by decreasing the head dimension which determines the width of a data track; typically this dimension is called the head "trackwidth".
In electromagnetic recording, thin film read and write heads are desirable because they provide narrow trackwidths and support high areal density. They are also easy to manufacture. With various thin film manufacturing techniques, such heads can be fabricated in batches on a substrate and then individuated.
A thin film write head includes pole pieces that are formed from thin films ("layers") of magnetic material. These layers are called "pole layers". In the pole tip region, the pole layers have a height dimension commonly called "throat height". In a finished write head, throat height is measured between an air bearing surface ("ABS") formed by polishing the tips of the pole layers ("pole tips") and a zero throat height level ("zero throat level") where a bottom pole layer (P1) and a top pole layer (P2) converge at the magnetic recording gap.
A thin film magnetic write head includes the pole tip region, which is located between the air bearing surface and the zero throat level, and a back region which extends back from the zero throat level to and including a back gap. The write head also has a yoke which includes the top and bottom pole layers, each pole layer having a pole tip in the pole tip region and a back portion in the back region. The pole layers are connected together at the back gap. An important manufacturing objective is to precisely define the pole tips of the write head thereby to maximize areal density. As is known, areal density is determined, in part, by the number of flux reversals per millimeter of track length, which in turn depends upon the length of the gap between the pole tips ("gap length"). By decreasing the gap length, the bit density within a track is increased. The shortness of the gap length is limited by the decreasing flux intensity between the pole tips. Therefore, efforts have been directed toward reducing the trackwidth of the write head, which is determined by the width of the pole layers in the pole tip region at the ABS.
The procedure for manufacturing a thin film magnetic write head in the prior art typically comprises forming a top pole layer after one or more insulation layers are formed on top of a coil layer. The insulation layers typically comprise resist material which is hardened in place by baking. During baking, resist layers flow forward and shrink backwards with respect to the pole tip region. The final configuration of the top insulation layer has a topography which slopes down toward the pole tip region. After depositing a seedlayer a thick resist layer is deposited. This layer is typically 10 microns or more thick. The resist layer follows the topography of the top insulation layer and builds structure in the pole tip region to a substantial thickness. The resist layer is then patterned by photolithography for the configuration of the top pole layer. During the photolithography step light penetrates the resist layer for patterning purposes. The thicker the resist layer the more this light scatters in a lateral direction, causing the edges of the photoresist pattern to be poorly defined. Because of this poor definition the narrowest pattern obtainable for the portion of the P2 pole layer which defines the second pole piece in the pole tip region is about 2 microns for a 4 micron thick plated pole tip. The next step is to plate the P2 pole layer and remove the photoresist. The result is a P2 pole tip with a width of about 2 microns which defines the trackwidth of the write head. It would be desirable if the trackwidth could be further still decreased so as to increase track density (TPI).
The challenge in building a head with a thin gap layer and narrow trackwidth is to minimize flux leakage, which increases as the gap length is reduced, and to avoid saturation, which occurs at lower flux levels with narrower pole tips. The first problem is alleviated by reducing the length of the pole tip region between ABS and zero throat level. The invention provides a solution to the second problem by avoiding saturation while providing a narrow trackwidth.